The metabolism of benzo(z)pyrene (BP) by human bronchus and pulmonary alveolar macrophages (PAM) from the same donor was studied to investigate whether the PAM might be useful as an indicator cell for the human bronchus. PAM were able to enzymatically convert BP into metabolites which bound to cellular macromolecules. The uptake of Fe2O3-BP into PAM and the release of BP and metabolites into the tissue media was determined. The effect of asbestos on this release is being investigated.